Reanalysis products often show discontinuities in the time evolution of analyzed fields, particularly for the derived variables, for example, precipitation. In the recently completed Climate Forecast System Reanalysis (CFSR) at the National Centers for Environmental Prediction, a sharp increase in the global mean precipitation around 1998 has been noted. A similar abrupt change also appears in several other reanalyses that have been recently completed. This sharp increase coincides with the introduction of the Advanced TIROS Operational Vertical Sounder (ATOVS) data into the assimilation system. Based on model simulations to complement the CFSR, this study analyzes the reason behind the sudden jump in precipitation. The outputs from both the CFSR and a simulation with the CFSR's atmospheric component model forced with the observed sea surface temperature and carbon dioxide concentration are used to understand the precipitation abrupt change in the CFSR. The analysis indicates that the change results from (1) the tendency of the forecast (during the assimilation cycle) to drift toward its mean state that is cooler and drier, (2) the tendency of the assimilation to correct the first guess forecast to a wetter analysis, (3) an analysis that the period after 1998 is in an even wetter mean state due to the ingestion of the ATOVS data, and (4) the combination of previous three factors resulting in a abrupt change in precipitation during the assimilation around 1998. The results presented here may also provide the developers of the reanalysis systems further insights about the possible causes for the change in precipitation around 1998.